Tiny animals are often the focus of discussions about marine life. Some of the smallest, plankton, are the basis of the marine food chain. They are the myriad species of microscopic plants and animals that we don’t see, but that we know are there making up a nutritious soup to supply other marine life with the nutrients they need, and about which I wrote last week in my column about water clarity and the role that plankton play in it. But, there’s another oddball tiny organism that has oft been in the limelight not because of ocean exploration, but because of its adventures in outer space – the little blind, gummy-bear like creature, the tardigrade.
There is something alluring about an animal that can live both in space and also in the deep ocean. It speaks to the amazing adaptations of living things – even the smallest ones. Your average tardigrade is less than a half-millimeter long. They aren’t particularly notable for their size, however, but instead for their ability to live under such a wide array of conditions. In space, they have been known to survive exposure to radiation and intense pressure changes. And, in water (both fresh and salt), they can survive an unusually wide array of temperature exposure from being frozen to being boiled.
Tardigrades are plump little creatures with segmented bodies and flattened heads whose name, tardigrada, means “slow stepper” for the waddling way they move on their four sets of clawed legs. They are also called water bears or moss piglets, both appropriately descriptive of their look. They are simple animals that don’t have proper circulatory or respiratory systems, but instead get oxygen from the water around them through their skin. They do, however, have digestive systems complete with tiny piercing mouthparts that help them to slurp up fluids from plants, algae and fungus — and even sometimes other tardigrades.
The key to their seeming invincibility is the ability to enter a slowed down state known as cryptobiosis or “tun”. They tuck their legs in on themselves, curl up into a little ball, and squeeze out the water from their bodies. Then, they form a glass-like cocoon around their shells that allows them to protect their bodies inside. This dried ball of tardigrade may seem like it is no longer alive, as its body’s activity is slowed down to 0.01% of its normal level, but it can re-emerge from this state by taking up water again once environmental conditions improve. This has allowed them to survive all five mass extinctions on Earth since their evolution nearly a half-billion years ago.
Although tardigrades have been found in outer space, they have also been found closer to home. In fact, a new species, Echiniscoides wyethi, was discovered among a sample of barnacles from Allen’s Island off the coast of Maine in 2014 by a group of students from Unity College. The newest of over 1,100 known species of tardigrades, was celebrated at the International Symposium on Tardigrada in Modena, Italy.
You, too, can look for tardigrades on Maine’s beaches at low tide. Apparently, the best way to collect them is to sample just under the surface of the sand and then “shock” your sample with freshwater to make the little tardigrades let go of the sand particles they like to hold on to so that they are more visible under a microscope. I haven’t tried this and am guessing that this time of year is likely not the best for tardigrade hunting, but I’m hoping to maybe find some in the spring. From space to the coast of Maine, these odd creatures help us to better appreciate the adaptations that make life along the coast possible.
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